Mapping of cardiac potentials and activation sequences by recording simultaneously from many electrodes applied directly to the heart promises to be a powerful tool for the study and treatment of arrhythmias. Several major improvements in mapping must be made if it is to fulfill this promise. The goal of this application is to perform the research and development necessary to bring about these improvements. 1. A computer- assisted mapping system will be constructed capable of recording from 512 channels simultaneously at an effective sampling rate of 15,000 Hz. Such a system is needed to map the complex activation sequences and high-frequency Purkinje spikes that can occur during some arrhythmias. 2. Improved methods will be developed to construct electrodes reliably, accurately, quickly, inexpensively, and in large numbers using microelectronic techniques. 3. Fast, accurate methods will be developed to specify the three-dimensional location of epicardial, intracavitary, and plunge electrodes for animal mapping. Computer graphics will be developed to display activation sequences as lines for the endocardium and epicardium or as surfaces in a three-dimensional representation of the thickness of the ventricular wall within seconds of recording the potentials. The lines or surfaces will be animated to move through the heart with time as in a movie. 4. Robust, quantitative algorithms for detection of the presence and timing of activation from electrode recordings will be developed and will be implemented in software to perform rapidly and with a minimum of human intervention. The data to develop these algorithms will be obtained from experiments in which the presence or absence of activation is known by means independent of the electrode recordings. 5. Experiments will be performed to determine the anatomic and electrical causes of fractionated potentials in cardiac electrode recordings, i.e., cases in which a single, discrete activation complex is not recorded. 6. Methods will be developed to estimate potentials away from the recording electrode sites in those regions in which it is not possible to place electrodes. Examples include estimating endocardial potentials from intracavitary recordings, epicardial potentials from recording from the overlying epicardial fat, and potentials through the ventricular wall from intracavitary and epicardial recordings. The accomplishment of these goals will greatly improve cardiac mapping and should lead to new advances in both the basic understanding and the clinical treatment of cardiac arrhythmias.